This invention relates generally to chucking apparatus for fixing a member to be rotated to a rotatable driving member and, more particularly, to such chucking apparatus which utilizes centrifugal force in connection with such fixation.
Chucking apparatus of the type wherein members having cylindrical shafts or bores are fixed for rotation with driving members by clamping devices which are guided in a cage member under the action of centrifugal force are known For example, see the chucking apparatus illustrated in the publication Konstruktion 29 (1977), Issue 2, Page 59, Picture 10 of March 24, 1977.
In conventional centrifugal chucking apparatus, the member to be rotated, which may comprise a tool or workpiece, has a cylindrical shaft or bore and is fixed for rotation with a driving member, which may comprise an outer hollow cylindrical member or an inner solid shaft or mandrel by clamping bodies associated with the driving member which engage the rotated member under the action of centrifugal force resulting from the rotation of the driving member. Thus, in the case where the rotated member has a cylindrical shaft, the driving member usually comprises a hollow cylindrical member in whose bore the rotated member is located for engagement by the clamping bodies which move inwardly under centrifugal force to engage the outer surface of the rotated member. Similarly, in the case where the rotated member has a hollow bore, the driving member is usually a mandrel which is located within the bore so that the clamping bodies move outwardly under centrifugal force to engage the inner surface of the rotated member.
However, such prior art centrifugal chucking apparatus are not entirely satisfactory for several reasons. Thus, generally, in such conventional chucking apparatus, the clamping bodies are usually pre-stressed so that they engage the rotated member even absent rotation of the driving member. Thus, removal of the rotated member from the driving member, such as when the tool or workpiece is changed, the clamping bodies frictionally engage the surface of the rotated member to be chucked thereby causing deleterious wear and deterioration of the surface of the clamping body which normally engages the rotated member.
Additionally, it has been found that during rotational acceleration of the driving member and associated rotated member, the engaging force exerted by the centrifugally operated clamping bodies on the rotated member tends to diminish. This appears to be a result of the tendency of the clamping bodies to rise or lift-off from their desired clamping locations. This diminished clamping force often results in slippage of the rotated member with respect to the driving member. Similar problems are also encountered in the operation of conventional centrifugal chucking apparatus when subjected to vibrations during operation. Thus, when the rotated member comprises a workpiece, the vibrations set up therein worked upon by a tool often causes a reduction in the clamping force exerted by the clamping bodies on the workpiece. These effects also appear in the case where the rotated member comprises a tool.
Centrifugal chucking apparatus have been proposed wherein the clamping bodies have been designed so that their centers of gravity are located outside of the axis of rotation in a manner such that during rotation, the clamping bodies are subjected to a tilting movement or torque which is intended to supplement the usual clamping force. However, even supplemented by the above provisions, in view of the unfavorable lever ratios present in such apparatus, the clamping force is still found to be inadequate to overcome the problems described above including the slippage which occurs during, for example, a machining process.